Rayon manufacture



Patented May 18, 1943 ESPATENT OFFICE,

' RAYON MANUFACTURE Arthur r. F. Mothwuri', Philadelphia, Pa., asslgnor,by mesne assignments, to Imperial Bay'- on Corporation, Gloucester, N.1., a corporation of Delaware No Drawing. Application October 5, 1940,

serial No. 359,901

7 Claims.

This invention relates to the manufacture of artificial fibres or otherregenerated cellulose products by the cuprammonium process and has as,its particular object a novel method oi. regenerating cellulose from itscuprammonium solutions.

A further object of this invention is to effect this regeneration byfewer operations than were,

which it is readily removed from the thread by subsequent washing, towhich components neutral salts for physically influencing coagulationmay be added.

As substances or the first description we select metallic salts whichattract ammonia to enter therewithinto compounds 01 higher stabilitythan the copper-ammonia-cellulose complex. Such salts for instance are:

heretofore, considered necessary.

Another important object of this invention is to lower the cost of thecuprammonium process.

Still other objects and advantages, inherent to the features andpractice 01' .our invention, will more fully appear in the followingexplanation:

When regenerating cellulose from cuprammonium cellulose solutions, forexample in the production of artificial fibres, the treatment ortreatments'to be employedprior to flnal washing have to serve the twopurposes liberating their ammonia contentand of converting coppercontent into a readily removable solution. i It is obvious thatapplication 01 acids, by neu-' tralizing ammonia and by dissolvingcopper, can take care of .both purposes. However, experience has shownthat the action of acids is-too rapid and that the ensuing thread isstiff and brittle and invariably uneven in structure and afllnity fordyes.

Practice has, therefore, turned to other means of precipitation with ,aresulting preference ior caustic soda in more or less diluted form.

Caustic, in contact with the spinning. solution, expels ammonia from thesoluble copper ammonia cellulose complex, and deposits most of thecopper content of the latter as insoluble copper hy- 35 droxide withinthe coagulating thread which leaves the precipitating bath in a highlyhydrated,

Copper salts, zinc salts, calcium chloride, sulphate of alumina, etc. I

Components of the second escription must be able to function'as solventsforcopper hydroxide in an alkaline solution. Ammonia salts, salts ofoxycarbonic acids, like glycolates,tartrates, ci-

' trates, etc., or glycerine and its homologues,

sugars and others can serve this purpose.

It is the substance or this invention, that no satisfactory results are,obtained by combining representatives of the two groupsindiscriminately, but that the respective components have to be selectedand proportioned with careful consideration of possible interreactions.

The following instance is meant to convey a clearer conception oi thisimportant point:

In practice, I preier, for the sake of economy, to apply a combinationof copper sulphate and ammonium sulphate.

Copper sulphate, acting as component or the first description, absorbsammonia, whereby the reaction goes successively through the followingtwo. stages:

which stages account for the-tact. that in the presence otsufllci'entammonia salt,- copper sulsemi-plastic state so that en acid treatmenthasa e wilf' ra am ni f m h into'iollow in order to tree it from copperand to termedla e precip t pp r mm r 80 complete its deflation andsetting. i ble coppertetramine sulphate.

Comparedwith the course oi. an acid precipit'a- T w q C P Q by he s ondformula tion, such proceeding adds at least one more opqualifiesammonium Sulphate h cm eration and additional expenses for caustic andsolvent r m ydr xide. v sulphuric acid which a one-stage coagulationWhile it further implies that ammonium sulwould avoid. phate alone mayact, in a chemical sense, a The present inventionprovidesa non-acid'preone stage precipi n r cum-ammonium cellu cipltating bath whichbiiersall the benefits oi lose solutions. such action is, in-pm ce. prediasingle treatment and eliminates atthe same .cated on the ratio orammonia to copper hydroxtime the defects andinbonveniencea'which the i nnts t e spinnin solution being p- I application ,oiireesacid andsubsequent neutrali- 801 0 38 t M9 B8 stipulated bra ove ditssationwould involve. I W" tion or0.85,to 1. i i J In principle, thecomposition of the new p'r'e- Bucha oonditionis not applicable toour-case: eipitatingbh comprises two active components with allcuprammonlum cellulosesolutions that or which the'flrstisabietoabsorbammonia, while the second has to, dissolve copper toja, form in duces alarge excess or against hi h ratio is much higher '(1.5'-1.8 to. 1 Itintrocoagulating action of ammonium sulphate alone cannot materiallydevelop beyond the purely physical effect of a salt solution.

To direct it'deilnitely along the desired chemical line the presence ofcopper sulphate has been found expedient and effective. It engages theexcess of ammonia and, thereby, leaves ammonium sulphate free toexercise its function as a solvent for copper hydroxide.

It can be seen that the amount of copper sulphate must be justsuflicient to convert the prevailing surplus ofammonia into coppertetramine sulphate, in other words-and this is one and to. prevent itsprecipitation byadding a corresponding amount of glycerine or corn syrupwhich addition has the further advantage of assisting in the removal ofcopper from the thread in the subsequent washing.

It will be further seen, that there is a minimum amount of sulphate ofammonia required as solvent, but that there is no limitation to anyreasonable increase above that minimum amount; in fact, the margin leftfor the percentage of this component or for any neutral salt in itsstead represents one of the various means of modifying coagulation. Asthe rate of diffusion rises with increasing temperature, another meansof modification consists in the temperature at which the precipitatingliquor is applied. Also other suitable additions such e. g. as favor orprevent deflation may be made.

The problem of reconditioning the withdrawn precipitating liquor forrepeated use, which is of great consequence from an economical point ofview, offers no difficulty; during the course of the reaction the entireammonia and copper content of the spinning solution has been converted ainto copper tetramine sulphate.

The latter is subject to the following reactions: I

soimnmcu-i-msoi omen), 2S04(NH4 )2 ment a portion of the liquor,equivalent to said increase, is definitely withdrawn and treated forrecovery of ammonia. For the balance enough copper hydroxide or basiccopper sulphate is dis lowered by forcing the acid. a

Economies effected by this method as compared with the favorite twostage caustic precipitation are substantial. Of the chemicals used inthe two stage process there are saved the total of caustic, that part ofthe sulphuric which is required for its neutralization and the use ofany additional chemicals for copper recovery. In addition, the one stagemethod creates conditions very favorable for reclaiming ammonlai Thougha combination of copper sulphate and ammonia sulphate for precipitationinvolves a maximum of economy, and is therefore the most interestingphase of this invention, its principle can be extended to othercombinations. 1

In giving instances of the manner in which this invention is carried outin practice, I relate them all to a spinning solution containing:

evaporation before adding I Percent Cellulose (100%) 4 Ammonia (100%)3.6 Copper hydroxide 2.4

to a spinning speed of 64 meters (71 yards) per minute and to 150 denieryarn.

Example #1 The precipitating bath is made up as follows:

It circulates at ordinary temperature at a rate of 500 cc. per jet andper minute.

Of the 3.6% ammonia contained in the spin ning solution, 2.76%represents what I have previously termed as excess ammonia.

The amount of copper sulphate is originally calculated to absorb thisexcess as copper tetramine sulphate. In the further course ofprecipitation the current requirements are established by tests and heldat the point where additional copper sulphate creates cloudiness byprecipitating copper hydroxide. Glycerine is added to provide forpossible fluctuations of the copper sulphate content of theprecipitating liquor.

- Duringcoagulation all available ammonia and copper hydroxide (exceptthat held in solution by the glycerine) is converted into coppertetramine sulphate.

Under proper consideration of the losses of liquid, through adhesion tothe thread and of the changes in volume, various methods may be employedfor conditioning the withdrawing precipi tating liquor for repeated use.

I prefer to proceed in the following manner: about one-eighth of thewithdrawn precipitating liquor is by-passed. To thebalance, which solvedin sulphuric and enough'water is-added to restore original concentrationof copper sulphate) as well as the original volume.

; Theoretically, the total amount of sulphuric this amount is less dueto loss of ammonia through adhesion to the thread, throughevapoacidhee'ded'should correspond to the ammonia content of thespinning solution-in practice,

. ration and other causes-and may be further 75 is recirculated, enoughsulphuric acid is contin-v B. .per minute and litre.

After the copper precipitate is removed by filtration or otherwise,enough copper sulphate solution and water is added to restore theprecipitating bath to its original volume and content of copper sulphateper litre.

-to be around 1.30 grams of sulphuric acid, 60

zation of fresh copper sulphate solution of known.

percentage in its restoration. This gives more accurate results thancould be obtainedby add-' ing first an amount of sulphuricacidsuflicient to precipitate all of the copper and then adding H T 5that part of the available ammonia originating,

more acid to dissolve that portion of the precipitated copper needed forrecirculation. I The by-passed portion is freed oi the copper by acid,is neutralized with'lime and is subjected to distillation for therecovery of ammonia.

The wash waters are treated for copper recovery only.

It circulates at a temperature of 40-45 C. (IMF-113 F.) and at a rate or500 cc. per min ute perjet.

The reactions which take place are similar to those of thepreceding-example; copper is dissolved to copper tetramine saltwhile-ammonia combines with calcium chloride, so that reconditioning ofthe withdrawn liquor can be efiected by muriatic acid.

It is, however, more advantageous in the case of recovery to precipitatethe copper as copper sulphide, preferably with calcium sulphydrate,

and to force evaporation of ammonia so that the acid is not the only wayof reconditioning the withdrawn precipitating liquor. There are otherpossibilities as, for instance, removal of the excess or total coppercontent as copper sulphide,

' basic copper carbonate, etc. or evaporation or ammonia may be forcedto efiect precipitation of copper and to lower consumption of sulphuric.acid or any one or these various methods may be used in conjunctionwith others.

the spinning maintained at a constant chemical ratio to the ammoniaconcentration or the spinning solution, said ratio being such thatsubstantially the whole of the ammonia contentnot otherwise consumed orlost during the reaction will be; absorbed by said copper sulphate.-

3. Process according to claim 1, in which-the copper sulphate isintroduced slightly in excess of that quantity substantially sufficientto bind from the spinning solution that is not otherwise consumedduring'the reaction, saidexcess resulting in a precipitate-said ammoniumsulphate being introduced to keep in solution said precipitate producedby the excess onsaid first component.

r 4. Process according to claim 1 in which the 7 Example #2 Theprecipitating bath is made up as follows:

Grams Chloride 0f flmmflflil 150 Chloride of calcium -e 2.4 Glycerine;per 1,000 cc .25

temperature of the precipitating bath is kept be-' tween and 60. C.

5. Process of regenerating cellulose from a cuprammonium solution in asingle stage which consists in spinning a cuprammonium solution in aprecipitating bath comprising, besides water as a solvent, twochemically active components of which the first component is coppersulphate 4 and the second component is ammonium 'sulphate, and thecopper sulphate is not consequentially more than the amount necessary toThere are and will be'yet other modiflcations of my process at my handsand atthe' hands of others. Each and all of the modifications whichconform to its generic spirit are intended to be protected to me throughthis patent application at large, irrespective of the circumstantialterminology of the claims appended.

What is claimed is:

l. The process of regenerating cellulose from its cuprammonium solutionsin a single stagewhich consists in spinning the cuprammonium solution inan alkaline precipitating bath, which bath comprises, besides water as asolvent, two chemically active components, or which one is a coppersulphate for attracting. and. absorbing absorb as copper tetraminesulphate that part of the ammonia content of the spinning solution whichis not consumed in dissolution of the copper hydroxide oi the spiningsolution by the ammonium sulphate lost.

6,.Process of regenerating cellulose from its cuprammonium solutionwhich comprises the step of precipitating and decoppering in singlevstage by the use of a spining bath substantially the entire body ofwhich is during the spinning l continuously in a non-acid condition,which process comprises the further step of withdrawing at least part ofthe precipitating liquor containing copper sulphate and water and thewithdrawn used precipitating liquor is reconditioned for re-circulation,said process comprising the addition oi. suflicientsulphuric acid toprecipitate all its copper content, the process'comprising the furtherstep of withdrawing for ammonia recov cry a portion or the liquor thatcontains the total gain in ammonium salt due to the use of the bath, andthe" process comprising the step of restoring the remainder of theliquor to the composition and volume which the original precipitatin'gbath possessed before its use, by the addition of copper sulphate andwater.

. 'I. Process of regenerating cellulose from its cuprammonium solutionin which precipitation and decopperin'g are carried out iniasingle stageby means of one spinning bath, which bath con- .tains copper sulphateand water, the process comprising the step of withdrawing precipitatingliquor and reconditioning it for re-use by forcing precipitation ofcopper'hydroxide and evaporationot ammonia to the extent of the gain inammonia and the other 01 which isammonium copper and ammonia from theimmediately preceding use, removing the precipitated copperhydroxide-and restoring the liquor to its orig'-. inal composition andvolume by the addition of.

copper sulphate and water as necessary.

ARTHUR l'. P. MO'I'HWURF.

concentration or the coppersulphate is during v

